Piraeus has been the port of Athens since antiquity, and it is still where you catch most island boats and cruise ships. What's confusing is that Piraeus has three harbors: Megas Limani (Main Harbor), where you'll see everything from tankers to cruise ships; Zea Limani (Zea Marina), the port for most of the swift hydrofoils that dart to the islands; and Mikrolimano (Little Harbor), also called Turkolimano, or Turkish Harbor by the old-timers, one of the most charming and picturesque harbors in the Mediterranean, lined with a number of fish restaurants, cafes, and bars.
The absence of helpful signs at both the Main Harbor and Zea Limani, however, along with their constant bustle, means that this is not an easy place to navigate. To be on the safe side, even if you have your tickets, get there an hour before your ship is scheduled to sail -- and don't be surprised if you curse this advice because your ship sails later than announced.
As in antiquity, today's Piraeus has the seamier side of a sailors' port of call as well as the color of an active harbor -- both aspects, somewhat sanitized, were portrayed in the 1960 film Never on Sunday that made Melina Mercouri an international star. Piraeus also has a sprawling street market just off the Main Harbor, where you can buy produce that arrives each day on island boats, including bread baked that morning on distant islands. If you find yourself here with some time to spare, take a stroll along Mikrolimano, Zea Marina (otherwise known as Pasalimani, with countless cafes and shopping stores), and the pretty residential area of Kastella.